Indoor Mite, Tyrophagus putrescenti

Macrophotograph of Live Mites

Definition/Function:

Tyrophagus putrescenti are also known as the common mold mite. These were raised on human whiskers in a humidity cabinet
over a saturated solution of sodium chloride. These mites are often found in homes, are strongly allergenic, but are not
detected by the common mite allergen tests.

Mites or their debris are found in indoor environments frequently. They all tend to be small ranging from about 40
micrometers to about a millimeter in largest dimension. They lay eggs and then develop through a number of intermediate
stages. The adult mite has 8 legs but the intermediate stages may have 2 to 8 legs, depending on the species and the stage.
All mites require a relative humidity above 50% but they will often occupy cooler parts of a home where the relative
humidity is naturally higher. They will also inhabit bedding and clothing where the relative humdity is elevated due to
the presence of the human body. Their prefered food varies by species. Many of them will survive on skin flakes.

Significance in the Environment:

Tyrophagus putrescenti was noted as causing health problems in humans as early as 1912 (Hughs, p. 42). Its allergenic
properties have been studied recently by Arlian et al. (below) and others.

There are over 124 different types of mites found in homes. Most of these are associated with allergies or asthma. The
standard tests for mite allergen can only detect 2 of the 124 mites that may be present. The collection efficiency of
a vacuum for even the 2 mites that could be detected is estimated at about 1%. Minor flucuation in that efficiency result
in variations of a factor of 20X (2000%). Part of this variation is due to the fact that the mite allergen is often
concentrated in a few large particles. The allergen of a few fragments would be swamped by the allergen associated with
one whole mite. Tapelifts of settled dusts in homes have been much more consistent in detecting mite problems.